[prev in list] [next in list] [prev in thread] [next in thread] 

List:       pykde
Subject:    Re: [PyQt] Patch fixing some const issues
From:       Phil Thompson <phil () riverbankcomputing ! com>
Date:       2017-08-11 21:08:23
Message-ID: 33D1F89D-F33B-4CB9-8BC7-AA8BDEE3926C () riverbankcomputing ! com
[Download RAW message or body]

On 11 Aug 2017, at 5:44 pm, oliver <oliver.schoenborn@gmail.com> wrote:
> 
> Without seeing the code this may be Irrelevant but one thing I remember about \
> autopointer is that it has move semantics. So for "a=b" with both being \
> autopointer, causes b to become an autopointer to null. B can be an autopointer to \
> const but cannot be a const autopointer.

Maybe the best thing is just to add an annotation that suppresses the generation of \
this particular helper. As this is using pointers it shouldn't be needed anyway.

Phil

> On Fri, Aug 11, 2017, 12:22 Shaheed Haque, <srhaque@theiet.org> wrote:
> On 11 August 2017 at 16:55, Phil Thompson <phil@riverbankcomputing.com> wrote:
> On 11 Aug 2017, at 4:37 pm, Shaheed Haque <srhaque@theiet.org> wrote:
> > 
> > 
> > 
> > On 11 August 2017 at 16:02, Phil Thompson <phil@riverbankcomputing.com> wrote:
> > On 11 Aug 2017, at 1:47 pm, Shaheed Haque <srhaque@theiet.org> wrote:
> > > 
> > > Hi,
> > > 
> > > Based on 4.19.4.dev1708081632, I see some issues with the emitted code \
> > > involving casts. There are several cases, but here is one example that \
> > > illustrates the issue: 
> > > ===  4.19.4.dev1708081632 output ===
> > > static void assign_std_auto_ptr_0100GpgME_EditInteractor(void *sipDst, \
> > > SIP_SSIZE_T sipDstIdx, const void *sipSrc) {
> > > reinterpret_cast< ::std::auto_ptr< ::GpgME::EditInteractor> \
> > > *>(sipDst)[sipDstIdx] = *reinterpret_cast<const ::std::auto_ptr< \
> > > ::GpgME::EditInteractor> *>(sipSrc); }
> > > ==============================
> > > 
> > > The above won't compile with errors boiling down, IIUC, to the fact that the \
> > > RHS has type "const something", and this is not compatible with the LHS which \
> > > has type "something" without the const. Now, I'll confess that I'm a bit rusty \
> > > on some of this, but I think the correct fix is to cast away the constness of \
> > > sipSrc earlier, like this: 
> > > === patched version ===
> > > static void assign_std_auto_ptr_0100GpgME_EditInteractor(void *sipDst, \
> > > SIP_SSIZE_T sipDstIdx, const void *sipSrc) {
> > > reinterpret_cast< ::std::auto_ptr< ::GpgME::EditInteractor> \
> > > *>(sipDst)[sipDstIdx] = *reinterpret_cast< ::std::auto_ptr< \
> > > ::GpgME::EditInteractor> *>(const_cast<void *>(sipSrc)); }
> > > ===================
> > > 
> > > Now, the LHS and the RHS match, and the compiler is happy. There are 4 similar \
> > > cases in gencode.c which I patched, as below. This patch also includes my diffs \
> > > for the static_cast<int>s from \
> > > https://www.riverbankcomputing.com/pipermail/pyqt/2017-August/039494.html. 
> > > (There is also one slightly different usage of reinterpret_cast<const ...> but \
> > > I am not sure if that is implicated or not).
> > 
> > I don't see why the RHS breaks the constness. Is std::auto_ptr doing something \
> > out of the ordinary? 
> > As I hinted, I'm well outside my comfort zone here, so take anything say with a \
> > pinch of salt. That said... 
> > It *might* well be auto_ptr-related, but I'm not sure, because the second \
> > paragraph on page http://en.cppreference.com/w/cpp/memory/auto_ptr seems to \
> > suggest that the RHS is being modified by the assignment (but that seems \
> > astonishing to me, so perhaps I am misreading it?). It is also true that all of \
> > the other templated types I am trying to support work fine in this regard. 
> > At any rate, the voluminous errors that result all seem to point to the \
> > assignment itself being bad, and to my simple-minded thinking, the problem is \
> > more that with the original formulation, the RHS is a const-qualified type, while \
> > the LHS is not.
> 
> Yes but the expression is making a copy of the object on the RHS so the mis-match \
> shouldn't make a difference. 
> My reading is that the documentation saying that the RHS is changed by the \
> assignment, and that the const is interfering with that! 
> Phil
> 
> _______________________________________________
> PyQt mailing list    PyQt@riverbankcomputing.com
> https://www.riverbankcomputing.com/mailman/listinfo/pyqt
> -- 
> Oliver
> My StackOverflow contributions
> My CodeProject articles
> My Github projects
> My SourceForget.net projects

_______________________________________________
PyQt mailing list    PyQt@riverbankcomputing.com
https://www.riverbankcomputing.com/mailman/listinfo/pyqt


[prev in list] [next in list] [prev in thread] [next in thread]